Tone reordering in a wireless communication system

ABSTRACT

One or more LDPC encoders generate two or more LDPC code words to be included entirely in an OFDM symbol. A frequency segment parser parses content of the two or more LDPC code words into a first frequency segment corresponding to a first subband of the communication channel and a second frequency segment corresponding to a second subband of the communication channel. A constellation mapper maps first content of the two or more LDPC code words to first constellation points corresponding to first OFDM tones in the first subband, and maps second content of the two or more LDPC code words to second constellation points corresponding to second OFDM tones in the second subband. A tone ordering unit reorders the first OFDM tones and the second OFDM tones such that the first content is distributed over the first subband, and the second content is distributed over the second subband.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/225,319, entitled “Tone Reordering in a Wireless CommunicationSystem,” filed on Aug. 1, 2016, which is a continuation of U.S. patentapplication Ser. No. 13/250,661, now U.S. Pat. No. 9,407,406, entitled“Tone Reordering in a Wireless Communication System,” filed on Sep. 30,2011, which claims the benefit of the following U.S. Provisional patentapplications:

U.S. Provisional Patent Application No. 61/390,833, filed on Oct. 7,2010;

U.S. Provisional Patent Application No. 61/392,430, filed on Oct. 12,2010; and

U.S. Provisional Patent Application No. 61/405,109, filed on Oct. 20,2010.

The disclosures of all of the patent applications referenced above arehereby incorporated by reference herein in their entireties.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to communication networks and,more particularly, to tone reordering in a wireless communication systemthat utilizes multiple tones or subchannels in a communication channel.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Development of wireless local area network (WLAN) standards such as theInstitute for Electrical and Electronics Engineers (IEEE) 802.11a,802.11b, 802.11g, and 802.11n Standards, has improved single-user peakdata throughput. For example, the IEEE 802.11b Standard specifies asingle-user peak throughput of 11 megabits per second (Mbps), the IEEE802.11a and 802.11g Standards specify a single-user peak throughput of54 Mbps, and the IEEE 802.11n Standard specifies a single-user peakthroughput of 600 Mbps. Work has begun on a new standard, IEEE 802.11ac,that promises to provide even greater throughput.

SUMMARY

In one embodiment, generating, at a communication device, a physicallayer (PHY) data unit for transmission via a communication channel,including generating orthogonal frequency division multiplexing (OFDM)symbols to be included in the PHY data unit, wherein generating each ofsome of the OFDM symbols includes: encoding, at a communication device,information bits to be included in the OFDM symbol to generate two ormore low density parity check (LDPC) code words to be included entirelyin the OFDM symbol. The method also includes parsing, at thecommunication device, content of the two or more LDPC code words into aplurality of data streams. The method further includes, for each datastream: parsing, at the communication device, the data stream into afirst frequency segment corresponding to a first subband of thecommunication channel and a second frequency segment corresponding to asecond subband of the communication channel, for the first frequencysegment, mapping, at the communication device, first content of the twoor more LDPC code words to first constellation points corresponding tofirst OFDM tones in the first subband of the communication channel, forthe first frequency segment, reordering, at the communication device,the first OFDM tones such that the first content of the two or more LDPCcode words is distributed over the first OFDM tones within the firstsubband of the communication channel, for the second frequency segment,mapping, at the communication device, second content of the two or moreLDPC code words to second constellation points corresponding to secondOFDM tones in the second subband of the communication channel, and forthe second frequency segment, reordering, at the communication device,the second OFDM tones such that the second content of the two or moreLDPC code words are distributed over the second OFDM tones within thesecond subband of the communication channel.

In another embodiment, an apparatus comprises a wireless networkinterface device configured to generate a physical layer (PHY) data unitfor transmission via a communication channel, including generatingorthogonal frequency division multiplexing (OFDM) symbols to be includedin the PHY data unit. The wireless network interface device isimplemented on one or more integrated circuit (IC) devices. The wirelessnetwork interface device includes: one or more low density parity check(LDPC) encoders, implemented on the one or more integrated circuit (IC)devices, the one or more LDPC encoders configured to encode informationbits to be included in an OFDM symbol to generate two or more LDPC codewords to be included entirely in the OFDM symbol; a stream parserimplemented on the one or more IC devices, the stream parser configuredto parse content of the two or more LDPC code words into a plurality ofdata streams; and a segment parser system implemented on the one or moreIC devices, the segment parser system coupled to the stream parser,wherein segment parser system is configured to, for each data stream,parse content of the two or more LDPC code words into a first frequencysegment corresponding to a first subband of the communication channeland a second frequency segment corresponding to a second subband of thecommunication channel. The wireless network interface device alsoincludes a constellation mapping system implemented on the one or moreIC devices, the constellation mapping system configured to, for eachdata stream: for the first frequency segment, map first content of thetwo or more LDPC code words to first constellation points correspondingto first OFDM tones in the first subband of the communication channel,and for the second frequency segment, map second content of the two ormore LDPC code words to second constellation points corresponding tosecond OFDM tones in the second subband of the communication channel.The wireless network interface device further includes a tone orderingsystem implemented on the one or more IC devices, the tone reorderingsystem configured to, for each data stream: for the first frequencysegment, reorder the first OFDM tones such that the first content of thetwo or more LDPC code words is distributed over the first OFDM toneswithin the first subband of the communication channel, and for thesecond frequency segment, reorder the second OFDM tones such that thesecond content of the two or more LDPC code words are distributed overthe second OFDM tones within the second subband of the communicationchannel.

In yet another embodiment, a tangible, non-transitory computer readablemedium, or media, stores machine readable instructions that, whenexecuted by one or more processors, cause the one or more processors to:generate orthogonal frequency division multiplexing (OFDM) symbols to beincluded in a physical layer (PHY) data unit for transmission via acommunication channel, including: encoding, according to a low densityparity check (LDPC) encoding scheme, information bits to be included inan OFDM symbol to generate two or more LDPC code words to be includedentirely in the OFDM symbol, parsing content of the two or more LDPCcode words into a plurality of data streams, for each data stream,parsing content of the two or more LDPC code words into a firstfrequency segment corresponding to a first subband of the communicationchannel and a second frequency segment corresponding to a second subbandof the communication channel, for each data stream and for the firstfrequency segment, mapping first content of the two or more LDPC codewords to first constellation points corresponding to first OFDM tones inthe first subband of the communication channel, for each data stream andfor the first frequency segment, reordering the first OFDM tones suchthat the first content of the two or more LDPC code words is distributedover the first OFDM tones within the first subband of the communicationchannel, for each data stream and for the second frequency segment,mapping second content of the two or more LDPC code words to secondconstellation points corresponding to second OFDM tones in the secondsubband of the communication channel, and for each data stream and forthe second frequency segment, reordering the second OFDM tones such thatthe second content of the two or more LDPC code words are distributedover the second OFDM tones within the second subband of thecommunication channel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example wireless communication networkin which tone reordering techniques are utilized, according to anembodiment.

FIG. 2 is a block diagram of an example physical layer (PHY) processingunit, according to an embodiment.

FIG. 3 is a diagram illustrating tone reordering in an OFDM symbol,according to an embodiment.

FIG. 4 is a block diagram of an example PHY processing unit configuredto implement tone reordering, according to an embodiment

FIG. 5 is a block diagram of another example PHY processing unitconfigured to implement tone reordering, according to anotherembodiment.

FIG. 6 is a block diagram of another example PHY processing unitconfigured to implement tone reordering, according to yet anotherembodiment.

FIG. 7A illustrates an example of spatial stream bit distributioncombined with tone reordering, according to an embodiment.

FIG. 7B illustrates an example of spatial stream bit distributioncombined with tone reordering, according to an embodiment.

FIG. 8 is a block diagram of a PHY processing unit used for a compositechannel, according to one embodiment.

FIG. 9 is a flow diagram of an example method for generating an OFDMsymbol, according to an embodiment.

DETAILED DESCRIPTION

In embodiments described below, a wireless network device such as anaccess point (AP) of a wireless local area network (WLAN) transmits datastreams to one or more client stations. The data units transmitted bythe AP to the client stations are encoded using various coding schemes,according to various embodiments and/or scenarios. In some embodimentand/or scenarios, binary convolutional codes (BCC) are utilized forencoding data streams. Alternatively, in other embodiments and/orscenarios, the data streams are encoded using block-based codes, suchas, for example, low density parity check (LDPC) codes. An LDPC codegenerally distributes adjacent information bits or adjacent blocks ofinformation bits to nonadjacent locations within the coded stream,according to an embodiment. However, in some embodiments, an LDPC codeused for a particular channel bandwidth is not long enough to encompassall information bits transmitted in a corresponding channel, andconsequently, in some such embodiments, more than one codeword is usedto encode the data. As a result, in these embodiments, coded bitscorresponding to an LDPC code are transmitted over a fraction of spatialstreams and/or in a fraction of the channel bandwidth, and therefore,full frequency diversity is not achieved in these situations. In somesuch embodiments, a tone reordering technique is utilized to spreadcoded information bits corresponding to a codeword over the channelbandwidth, thereby allowing frequency diversity to be better utilized.

FIG. 1 is a block diagram of an example wireless local area network(WLAN) 10, according to an embodiment. An AP 14 includes a hostprocessor 15 coupled to a network interface 16. The network interface 16includes a medium access control (MAC) processing unit 18 and a physicallayer (PHY) processing unit 20. The PHY processing unit 20 includes aplurality of transceivers 21, and the transceivers 21 are coupled to aplurality of antennas 24. Although three transceivers 21 and threeantennas 24 are illustrated in FIG. 1, the AP 14 can include differentnumbers (e.g., 1, 2, 4, 5, etc.) of transceivers 21 and antennas 24 inother embodiments. In one embodiment, the MAC processing unit 18 and thePHY processing unit 20 are configured to operate according to a firstcommunication protocol. The first communication protocol is alsoreferred to herein as a very high throughput (VHT) protocol. In anotherembodiment, the MAC unit processing 18 and the PHY processing unit 20are also configured to operate according to at least a secondcommunication protocol (e.g., the IEEE 802.11n Standard, the IEEE802.11g Standard, the IEEE 802.11a Standard, etc.).

The WLAN 10 includes a plurality of client stations 25. Although fourclient stations 25 are illustrated in FIG. 1, the WLAN 10 can includedifferent numbers (e.g., 1, 2, 3, 5, 6, etc.) of client stations 25 invarious scenarios and embodiments. At least one of the client stations25 (e.g., client station 25-1) is configured to operate at leastaccording to the first communication protocol.

The client station 25-1 includes a host processor 26 coupled to anetwork interface 27. The network interface 27 includes a MAC processingunit 28 and a PHY processing unit 29. The PHY processing unit 29includes a plurality of transceivers 30, and the transceivers 30 arecoupled to a plurality of antennas 34. Although three transceivers 30and three antennas 34 are illustrated in FIG. 1, the client station 25-1can include different numbers (e.g., 1, 2, 4, 5, etc.) of transceivers30 and antennas 34 in other embodiments.

In an embodiment, one or all of the client stations 25-2, 25-3 and 25-4has a structure the same as or similar to the client station 25-1. Inthese embodiments, the client stations 25 structured the same as orsimilar to the client station 25-1 have the same or a different numberof transceivers and antennas. For example, the client station 25-2 hasonly two transceivers and two antennas, according to an embodiment.

In various embodiments, the PHY processing unit 20 of the AP 14 isconfigured to generate data units conforming to the first communicationprotocol. The transceiver(s) 21 is/are configured to transmit thegenerated data units via the antenna(s) 24. Similarly, thetransceiver(s) 21 is/are configured to receive data units via theantenna(s) 24. The PHY processing unit 20 of the AP 14 is configured toprocess received data units conforming to the first communicationprotocol, according to an embodiment.

In various embodiments, the PHY processing unit 29 of the client device25-1 is configured to generate data units conforming to the firstcommunication protocol. The transceiver(s) 30 is/are configured totransmit the generated data units via the antenna(s) 34. Similarly, thetransceiver(s) 30 is/are configured to receive data units via theantenna(s) 34. The PHY processing unit 29 of the client device 25-1 isconfigured to process received data units conforming to the firstcommunication protocol, according to an embodiment.

FIG. 2 is a block diagram of an example PHY processing unit 200configured to operate according to the VHT protocol, according to anembodiment. Referring to FIG. 1, the AP 14 and the client station 25-1,in one embodiment, each include a PHY processing unit such as the PHYprocessing unit 200.

The PHY unit 200 includes a scrambler 204 that generally scrambles aninformation bit stream to reduce an occurrence of long sequences of onesor zeros, according to an embodiment. In another embodiment, thescrambler 204 is replaced with a plurality of parallel scramblerslocated after an encoder parser 208. In this embodiment, each of theparallel scramblers has a respective output coupled to a respective oneof a plurality of FEC encoders 212. The plurality of parallel scramblersoperates simultaneously on a demultiplexed stream. In yet anotherembodiment, the scrambler 204 comprises a plurality of parallelscramblers and a demultiplexer that demultiplexes the information bitstream to the plurality of parallel scramblers, which operatesimultaneously on demultiplexed streams. These embodiments may beuseful, in some scenarios, to accommodate wider bandwidths and thushigher operating clock frequencies.

The encoder parser 208 is coupled to the scrambler 204. The encoderparser 208 demultiplexes the information bit stream into one or moreencoder input streams corresponding to one or more FEC encoders 212. Inanother embodiment with a plurality of parallel scramblers, the encoderparser 208 demultiplexes the information bit stream into a plurality ofstreams corresponding to the plurality of parallel scramblers.

Each FEC encoder 212 encodes the corresponding input stream to generatea corresponding encoded stream. In one embodiment, each FEC encoder 212includes a binary convolutional encoder. In another embodiment, each FEC212 encoder includes a binary convolutional encoder followed by apuncturing block. In another embodiment, each FEC encoder 212 includes alow density parity check (LDPC) encoder. In yet another embodiment, eachFEC encoder 212 additionally includes a binary convolutional encoderfollowed by a puncturing block. In this embodiment, each FEC encoder 212is configured to implement one or more of: 1) binary convolutionalencoding without puncturing; 2) binary convolutional encoding withpuncturing; or 3) LDPC encoding.

A stream parser 216 parses the one or more encoded streams into one ormore spatial streams for separate interleaving and mapping intoconstellation points. Corresponding to each spatial stream, aninterleaver 220 interleaves bits of the spatial stream (i.e., changesthe order of the bits) to prevent long sequences of adjacent noisy bitsfrom entering a decoder at the receiver. In one embodiment, interleavers220 are utilized only for data encoded using BCC encoding. Generally, ina data stream encoded using an LDPC code, adjacent bits are spread outby the code itself and, according to an embodiment, no furtherinterleaving is needed. Accordingly, in some embodiments, interleavers220 are omitted when LDPC encoding is used. On the other hand, inanother embodiment, for example if a particular code length is such thatdata bits are not spread out over an entire channel bandwidth, but arespread out over only a portion of the channel bandwidth, interleavers220 are utilized to further interleave the LDPC encoded bits. In someembodiments, however, interleaving LDPC encoded bits results inunnecessary added latency, and other techniques (such as tonereordering, described herein) are utilized to spread the coded bits overa bandwidth of a communication channel.

Also corresponding to each spatial stream, a constellation mapper 224maps a sequence of bits to constellation points corresponding todifferent subcarriers of an orthogonal frequency division multiplexing(OFDM) symbol. More specifically, for each spatial stream, theconstellation mapper 224 translates every bit sequence of length log₂(M)into one of M constellation points, in an embodiment. The constellationmapper 224 handles different numbers of constellation points dependingon the modulation and coding scheme (MCS) being utilized. In anembodiment, the constellation mapper 224 is a quadrature amplitudemodulation (QAM) mapper that handles M=2, 4, 16, 64, 256, and 1024. Inother embodiments, the constellation mapper 224 handles differentmodulation schemes corresponding to M equaling different subsets of atleast two values from the set {2, 4, 16, 64, 256, 1024}.

In an embodiment, a space-time block coding unit 228 receives theconstellation points corresponding to the one or more spatial streamsand spreads the spatial streams to a greater number of space-timestreams. In some embodiments, the space-time block coding unit 228 isomitted. A plurality of cyclic shift diversity (CSD) units 232 arecoupled to the space-time block unit 228. The CSD units 232 insertcyclic shifts into all but one of the space-time streams (if more thanone space-time stream) to prevent unintentional beamforming. For ease ofexplanation, the inputs to the CSD units 232 are referred to asspace-time streams even in embodiments in which the space-time blockcoding unit 228 is omitted.

In one embodiment, the frequency CSD values applied on each of fourspace-time streams are the same as the frequency CSD values specified inthe IEEE 802.11n Standard. In another embodiment, the frequency CSDvalues applied on each of four space-time streams are suitable valuesdifferent than the frequency CSD values specified in the IEEE 802.11nStandard. In one embodiment, if more than four space-time streams areutilized, the frequency CSD values are defined similarly to thedefinitions in the IEEE 802.11n Standard.

In one embodiment, the time CSD values applied on each of fourspace-time streams are the same as the time CSD values specified in theIEEE 802.11n Standard. In another embodiment, the time CSD valuesapplied on each of four space-time streams are suitable values differentthan the time CSD values specified in the IEEE 802.11n Standard. In oneembodiment, if more than four space-time streams are utilized, the timeCSD values are defined to be values within the range [−200 0]nanoseconds (ns). In another embodiment, if more than four space-timestreams are utilized, the time CSD values are defined to be valueswithin a suitable range different than the range [−200 0] ns.

A spatial mapping unit 236 maps the space-time streams to transmitchains. In various embodiments, spatial mapping includes one or moreof: 1) direct mapping, in which constellation points from eachspace-time stream are mapped directly onto transmit chains (i.e.,one-to-one mapping); 2) spatial expansion, in which vectors ofconstellation point from all space-time streams are expanded via matrixmultiplication to produce inputs to the transmit chains; and 3)beamforming, in which each vector of constellation points from all ofthe space-time streams is multiplied by a matrix of steering vectors toproduce inputs to the transmit chains.

Each output of the spatial mapping unit 236 corresponds to a transmitchain, and each output of the spatial mapping unit 236 is operated on byan inverse discrete Fourier transform (IDFT) calculation unit 240, e.g.,an inverse fast Fourier transform calculation unit, that converts ablock of constellation points to a time-domain signal. Outputs of theIDFT units 240 are provided to GI insertion and windowing units 244 thatprepend, to each OFDM symbol, a guard interval (GI) portion, which is acircular extension of the OFDM symbol in an embodiment, and smooth theedges of each symbol to increase spectral decay. Outputs of the GIinsertion and windowing units 244 are provided to analog and RF units248 that convert the signals to analog signals and upconvert the signalsto RF frequencies for transmission. The signals are transmitted in a 20MHz, a 40 MHz, an 80 MHz, a 120 MHz, or a 160 MHz bandwidth channel, invarious embodiments and/or scenarios. In other embodiments, othersuitable channel bandwidths are utilized.

According to an embodiment, the VHT protocol defines one or morespecific codewords to be used by the FEC encoders 212 when performingLDPC encoding. For example, in one embodiment, three possible codewordlengths are defined for the VHT protocol, and the specific codewordlengths are 648 bits, 1296 bits and 1944 bits. In another embodiment,only one of the 648 bits, 1296 bits, or 1944 bits codeword lengths isutilized. In other embodiments, one or more other suitable codewordlengths are defined. Generally, longer data units are encoded usinglonger codewords, in various embodiments and/or scenario, for examplewhen the particular MCS being utilized corresponds to a larger bandwidthand/or a higher number of spatial streams. In one embodiment, the LDPCcodes are defined as in the IEEE 802.11n Standard. In anotherembodiment, the LDPC codes are defined as in the IEEE 802.11n Standard,but using only one of multiple codeword lengths defined in the IEEE802.11n Standard. In another embodiment, one or more other suitable LDPCcodes are defined by the VHT protocol different than those defined bythe IEEE 802.11n Standard.

Generally, an LDPC code distributes consecutive coded bits throughout achannel bandwidth, and therefore, if a channel experiences adverseconditions in a portion the channel, the data can still be recovered atthe receiver due to error correcting nature of the code. In someembodiments and/or scenarios, however, an LDPC code used to encode adata stream is less than the number of information bits in acorresponding OFDM symbol, and, accordingly, in these embodiments and/orscenarios, the LDPC code distributes coded bits over only a portion ofthe channel. For example, in an embodiment, LDPC codes are defined as inIEEE 802.11n Standard and the longest available codeword length is,accordingly, equal to 1944. The number of coded bits in an OFDM symbol,on the other hand, is higher than 1944 in some situations, particularlywhen a large bandwidth channel (e.g., 80 MHz or a 160 MHz channel)and/or a large number of spatial streams (e.g., five or more spatialstreams) are being utilized. Accordingly, in at least some suchembodiments and/or scenarios, more than one codeword is used to generatean OFDM symbol, wherein each codeword corresponds to a portion of thecoded bits in an OFDM symbol. As a result, in such embodiments and/orscenarios, the LDPC coded bits are generally distributed over a numberof blocks of data tones, wherein the number of blocks corresponds to thenumber of codewords used to encode the data. Consequently, in suchembodiments and/or scenarios, frequency diversity is only partiallyutilized.

In some such embodiments, to ensure a better distribution of coded bitsover a channel bandwidth, tones in an OFDM symbol are reorderedaccording to a tone reordering scheme, and the coded data bits ormodulation symbols are mapped onto the reordered data tones fortransmission. More specifically, if more than one codeword is used togenerate an OFDM symbol, OFDM tones are reordered such that bits (orblocks of bits) corresponding to each codeword are mapped ontononconsecutive data tones in an OFDM symbol, wherein the distancebetween the tones onto which consecutive bits or blocks of bits aremapped is defined such that information bits corresponding to each ofthe codewords are distributed over the OFDM symbol.

FIG. 3 is a diagram illustrating tone reordering in an OFDM symbol,according to one such embodiment. Block 310 represents an OFDM symbolencoded using three codewords, wherein each codeword covers a respectiveportion of the OFDM symbol. More specifically, block 302 corresponds toa first codeword, block 304 corresponds to a second codeword, and block306 corresponds to a third codeword. Accordingly, as illustrated in FIG.3, data corresponding to each codeword is transmitted over thecorresponding portion of the channel bandwidth. In this situation, asdiscussed above, if a portion of the channel experiences adverseconditions, such as fading or scattering, the data corresponding to thecodeword in the affected portion of the channel may be greatlycompromised, generally resulting in decoding errors for that portion ofthe channel.

With continued reference to FIG. 3, in the OFDM symbol 320, OFDM tonesare reordered such that data bits (or modulation symbols) correspondingto each of the three codewords are distributed throughout the channelbandwidth. For example, as a result of tone reordering, data bitscorresponding to the first codeword are mapped to the data tonesrepresented by 302-1, 302-2, 302-3 and 302-4. Similarly, data bitscorresponding to the second codeword are mapped to the data tonesrepresented by 304-1, 304-2, 304-3 and 304-4, and data bitscorresponding to the third codeword are mapped to the data tonesrepresented by 306-1, 306-2 and 306-3. In this case, in an embodiment,if a portion of a channel experiences adverse conditions, datacorresponding to a part of each codeword, rather than data correspondingto a whole codeword is affected. As a result, in this case, due to errorcorrecting nature of the LDPC code, the corresponding data can berecovered at the receiver even in situations in which data transmittedin the portion of the channel is greatly compromised, in variousembodiments and/or scenarios.

In various embodiments, a PHY processing unit and/or a MAC processingunit, such as the PHY processing 20 and/or the MAC processing unit 18(FIG. 1), respectively, performs tone reordering at various locationswithin the processing flow. For example, now referring to FIG. 2, in oneembodiment, tone reordering is performed for each spatial stream at theoutputs of the spatial stream parser 216. As another example, in anotherembodiment, tone reordering is performed for each spatial stream at theoutput of the corresponding constellation mapper 224. In anotherembodiment, tone reordering is performed for each space-time stream atthe corresponding output of the space-time stream mapping unit 228. Inanother embodiment, tone reordering is performed for each space-timestream at the corresponding input to the spatial mapping unit 236. Inanother embodiment, tone reordering is performed for each space-timestream at the corresponding output of the spatial mapping unit 236. Inone embodiment, tone reordering for each space-time stream is performedby the corresponding IDFT unit 240. In other embodiments, tonereordering is performed at other suitable locations within a PHY and/ora MAC processing flow.

With continued reference to FIG. 2, as discussed above, the CSD units232 insert cyclic shifts into space time streams to preventunintentional beamforming effects. In some embodiments, the particularcyclic shift values corresponding to OFDM tones are defined differentlyfor at least some of the tones. Therefore, in these embodiments, if tonereordering is performed after cyclic shift insertion, in at least somecases, a mismatch exists between the applied CSD value and the CSD valuethat is defined for the particular channel over which the reordered OFDMtone is transmitted. This CSD value mismatch, in at least somesituations, leads to decoding errors on the receiving end. Accordingly,in an embodiment, CSD values are also reordered according to the samereordering scheme that is used to reorder the OFDM tones, and in thiscase, no mismatch exists between the applied CSD value and the valuedefined for the subcarrier channel used to transmit the tone.

Similarly, in an embodiment, spatial mapping unit 236 appliesbeamforming matrices to the OFDM tones, wherein the particular matrixapplied to an OFDM tone is based on the actual subcarrier channel overwhich the tone is transmitted. In this embodiment, if the OFDM tones arereordered after beamforming matrices are applied, applied beamformingmatrices will then not match the actual subcarrier channels over whichthe reordered tones are transmitted. This mismatch between beamformingcomponents and the transmission channel results in a decrease inperformance at the receiving end, such as, for example, a decrease insignal to noise ratio, a decrease in throughput, an increase in packeterror rate, etc. Accordingly, in one embodiment, beamforming matricesare also reordered according to the same scheme that is used to reorderthe tones, and in this case, the applied beamforming matrices match theactual channel used to transmit the reordered OFDM tone, and in thiscase, the desired beamforming effect at the receiving end is thereforeachieved.

In an embodiment, if tone reordering occurs after CSD insertion andafter the spatial mapping, both the CSD value reordering and thebeamsteering matrix reordering are performed.

In some embodiments, independent data corresponding to different clientstations are transmitted by an access point simultaneously, which ishereby referred to as multi-user transmissions. In some embodimentsutilizing multi-user transmissions, information data corresponding tothe different users is encoded using different encoding techniques. Forexample, in one embodiment, a particular data unit is a two-user unit,that is, this data unit includes independent data transmittedsimultaneously to two different client stations. In one such embodimentor scenario, BCC encoding is used to encode information bits for thefirst user (i.e., first client station), while LDPC encoding is used toencode information bits for the second user (i.e., second clientstation). In this embodiment, interleaving (e.g., by inerleavers 220 ofFIG. 2) is performed for the BCC encoded bits corresponding to the firstuser. On the other hand, for the LDPC encoded bits corresponding to thesecond user, interleaving is not utilized. On the other hand, tonereordering is used only for the OFDM tones corresponding to the seconduser, according to an embodiment. Accordingly, in an embodiment in whichtone reordering occurs after spatial mapping and/or after CSD insertion,the spatial matrices and/or cyclic shift values, respectively,corresponding to only the second user are reordered.

FIG. 4 is a block diagram of an example PHY processing unit 400configured to implement tone reordering, according to an embodiment. ThePHY processing unit 400 is similar to the PHY processing unit 200 (FIG.2), except that the PHY processing unit 400 includes a respective toneordering unit 422 coupled to each output of the spatial stream parser416. In the PHY processing unit 400, the encoder 412 receivesinformation bits to be included in an OFDM symbol and utilizes LDPCencoding to generate encoded information bits. In an embodiment, foreach spatial stream, the corresponding tone ordering unit 422 reorderscoded information bits or blocks of coded information bits according toa tone reordering function. The tone reordering function is generallydefined such that consecutive coded information bits or blocks ofinformation bits are mapped onto nonconsecutive tones in the OFDMsymbol. In an embodiment, the tone reordering function is defined suchthat two consecutive coded bits (or blocks of bits) are mapped onto OFDMtones that are separated by a minimum distance D. For example, in oneembodiment, the minimum distance D is defined as 3 OFDM tones, andaccordingly, in this embodiment, consecutive coded bits (or blocks ofbits), as a result of tone reordering, are separated by at least 3tones. In another embodiment, another suitable distance D (such as 2, 4,5, 6, etc.) is utilized.

In one embodiment, coded information bits are reordered in blocks ofconsecutive bits, wherein the blocks correspond to, for example,constellation points within a modulation symbol (corresponding to theMCS being utilized). In an embodiment, tone reordering of blocks ofinformation bits prior to constellation mapping is equivalent toreordering the corresponding modulation symbols after constellationmapping is performed.

FIG. 5 is a block diagram of another example PHY processing unit 500configured to implement tone reordering, according to anotherembodiment. The PHY processing unit 500 is similar to the PHY processingunit 400 of FIG. 4, except that in the PHY processing unit 500 tonereordering is performed for each space time stream at the correspondingoutput of the space-time block coding unit 528. In this embodiment, tonereordering is performed after information bits have been mapped toconstellation points. Accordingly, in this embodiment, the tone orderingunits 530 change the order of modulation symbols according to a tonereordering function such that the reordered modulation symbols aremapped to non adjacent data tones within the OFDM symbol.

FIG. 6 is a block diagram of another example PHY processing unit 600configured to implement tone reordering, according to anotherembodiment. The PHY processing unit 600 includes a tone reordering 638for each space-time stream at the corresponding output of the spatialmapping unit 636. Accordingly, in this embodiment, tone reordering isperformed after cyclic shift insertion is performed (by CSD units 632)as well as after spatial stream mapping is performed (by the spatialmapping unit 636). Accordingly, in this embodiment, cyclic shift valuesand spatial stream matrices are also reordered according to the functionused for reordering the corresponding OFDM tones, so that the appliedcyclic shifts and the applied steering matrices, respectively, match thechannels onto which the corresponding OFDM tones are mapped.

As an example of spatial mapping matrix reordering, in one embodiment,suppose a tone reordering function F(.) maps an input tone k to anoutput tone F(k). If there are N tones, in an embodiment, thecorresponding spatial mapping matrices without reordering arerepresented by {Q₁, Q₂, . . . , Q_(N)}. The reordered spatial matricesthen correspond to {Q_(F(1)), Q_(F(2)), . . . , Q_(F(N))}, according toan embodiment. Accordingly, in this embodiment, the output of thespatial mapping unit 636 is represented by {Q_(F(1))x₁, Q_(F(2))x₂, . .. , Q_(F(N))x_(N)}, where Q_(F(k))x_(k) is corresponds to spatiallymapped data transmitted on the f(k)_(th) tone. That is, in thisembodiment, as a result of spatial matrix reordering, a matrix appliedto an OFDM tone matches the channel over which the tone is transmittedafter tone reordering is performed.

In one embodiment, tone reordering operation is combined with thespatial stream parsing operation. For example, referring back to FIG. 2,in one embodiment, tone reordering is performed by the stream parser216. In this embodiment, the stream parser 216 assigns bits to differentspatial streams in an order that distributes coded bits corresponding toa codeword over spatial streams and over a channel bandwidth. FIG. 7Aillustrates one specific example of spatial stream bit distributioncombined with tone reordering, according to one embodiment. In thisexample embodiment, a stream parser assigns consecutive bits toconsecutive spatial streams, assigning one bit to each stream in onecycle according to the order illustrated in FIG. 7A. Similarly, FIG. 7Billustrates another specific example of spatial stream bit distributioncombined with tone reordering, according to another embodiment. In thisembodiment, a stream parser assigns consecutive bits to consecutivespatial streams, assigning two consecutive bits to each spatial streamin one cycle according to the order illustrated in FIG. 7B. In otherembodiments, the stream parser 216 assigns bits to different spatialstreams in a different suitable order that generally distributesconsecutive information bits over a channel bandwidth. In tonereordering implementation, as a result of combining tone reordering withspatial stream parsing, in an embodiment, no extra memory specificallyfor tone reordering is utilized.

In some embodiments, a particular channel is a composite channel that isprocessed at least partially in two or more individual channels. Inother words, in this embodiment, the composite channel comprises two ormore individual channels, and the individual channels are processedindividually. For example, in an embodiment, an 80 MHz channel isprocessed at least partially using two 40 MHz portions. As anotherexample, a 160 MHz channel is processed at least partially using two 80MHz portions, according to another embodiment. In some such embodiments,tone reordering techniques described herein are utilized for each of theindividual channels. Depending on the location of the tone ordering unitwithin the PHY processing flow, in some embodiments, a separate toneordering unit performs tone reordering for each of the individuallyprocessed channels, while in other embodiments a single tone orderingunit is used for the composite channel. Further, in an embodiment inwhich tone ordering is performed, for each of the individual channels,after spatial mapping, the spatial mapping matrices are reorderingjointly for the entire composite channel. In an embodiment, jointreordering of the spatial mapping matrices ensures that OFDM tones areaccurately mapped in a situation in which a tone from one individualchannel is mapped to a tone in another individual channel.

FIG. 8 is a block diagram of a PHY processing unit 800 used for acomposite 160 MHz channel, according to one embodiment. The PHYprocessing unit 800 includes a stream parser 802 that parses coded databits into a number of spatial streams. Corresponding to each spatialstream or space-time stream, a tone ordering unit 804 performs OFDM tonereordering to distribute coded bits across the composite channelbandwidth. Also corresponding to each spatial stream, a frequency parser806 parses coded and reordered bits into a first channel portion 808 anda second channel portion 810 (in this case, each portion correspondingto an 80 MHz subband. For ease of explanation, FIG. 8 shows a frequencyparser 806, a bit interleaver 808 corresponding to a first channelportion, and a bit interleaver 810 corresponding to a second channelportion for only one of the spatial streams or space-time streams,however, in some embodiments, a frequency parser 806, a first bitinterleaver 808, and a second bit interleaver 810 are included for eachspatial stream.

Each bit interleaver 808 and 810 further interleaves the encoded andreordered bits, according to one embodiment. In another embodiment, abit interleaver is only used for BCC encoded data bits, and not used forLDPC encoded data. In this embodiment, the bit interleavers 808, 810 areomitted in embodiments and/or scenarios utilizing LDPC encoding.Similarly, tone ordering units 804 are used only for data encoded usingLDPC encoding in some embodiments. Accordingly, tone ordering units 804in some embodiments and/or scenarios utilizing BCC encoding are omitted.

In one embodiment utilizing composite channel processing, tonereordering is combined with spatial stream parsing. In anotherembodiment utilizing composite channel processing, tone reordering iscombined with frequency parsing. Accordingly, in this embodiment,frequency parsing is defined such that the coded bits are distributedover the composite channel bandwidth.

FIG. 9 is a flow diagram of an example method 900 for generating an OFDMsymbol, according to one embodiment. The method 900 is implemented bythe network interface 16 (e.g., the PHY processing unit 20 of FIG. 1),in an embodiment. The method 900 is implemented by the network interface27 (e.g., the PHY processing unit 29 of FIG. 1), in another embodiment.In other embodiments, the method 900 is implemented by other suitablenetwork interfaces.

At block 904, information bits to be included in the OFDM symbol areencoded using one or more encoders. In one embodiment, information bitsare encoded at block 904 using binary convolutional coding (BCC). Inanother embodiment, information bits are encoded at block 904 using alinear parity check code (LDPC). In one embodiment utilizing LDPCencoding, more than one codeword is needed to encode all informationbits to be included in an OFDM symbol. In some embodiments, the OFDMsymbol includes information to be transmitted simultaneously to morethan one user. In one such embodiment, the information intended for afirst user is encoded at block 904 using BCC, while information for asecond user is encoded at block 904 using LDPC. In other embodiments,information is encoded at block 904 using other suitable codingtechniques.

At block 908, the encoded information bits are parsed into a pluralityof spatial streams. In an embodiment, a plurality of space-time streamsis generated from the plurality of spatial streams using a space-timeblock coder (not shown in FIG. 9). In another embodiment, space-timeencoding is not utilized. At block 912, the spatial streams orspace-time streams are mapped to transmit chains using a plurality ofspatial stream matrices, wherein each spatial stream matrix correspondsto an OFDM tone in the symbol. In one embodiment, spatial streammatrices are beamforming matrices used to steer a data unit in thedirection of the intended receiver. In other embodiments, spatialstreams are mapped to transmit chains using other suitable spatialmapping techniques.

At block 914, OFDM tone reordering is performed. In an embodiment, tonereordering is performed for tones onto which LDPC encoded bits aremapped in order to distribute consecutive coded bits or block of bitsover a channel bandwidth. In another embodiment, tone reordering isalternatively or additionally performed for OFDM tones onto which BCCcoded bits are mapped. In other embodiments tone reordering is performedfor tones corresponding to information bits encoded using other suitablecoding techniques. In an embodiment, if tone reordering is performedafter spatial mapping, then the corresponding spatial matrices are alsoreordered prior to applying the mapping matrices to the OFDM tones. Onthe other hand, in an embodiment, if tone reordering is performed beforespatial mapping, that is, if the order of blocks 912 and 914 isinterchanged, then spatial matrix reordering at block 914 need not beperformed.

At least some of the various blocks, operations, and techniquesdescribed above may be implemented utilizing hardware, a processorexecuting firmware instructions, a processor executing softwareinstructions, or any combination thereof. When implemented utilizing aprocessor executing software or firmware instructions, the software orfirmware instructions may be stored in any computer readable memory suchas on a magnetic disk, an optical disk, or other storage medium, in aRAM or ROM or flash memory, processor, hard disk drive, optical diskdrive, tape drive, etc. Likewise, the software or firmware instructionsmay be delivered to a user or a system via any known or desired deliverymethod including, for example, on a computer readable disk or othertransportable computer storage mechanism or via communication media.

Communication media typically embodies computer readable instructions,data structures, program modules or other data in a modulated datasignal such as a carrier wave or other transport mechanism. The term“modulated data signal” means a signal that has one or more of itscharacteristics set or changed in such a manner as to encode informationin the signal. By way of example, and not limitation, communicationmedia includes wired media such as a wired network or direct-wiredconnection, and wireless media such as acoustic, radio frequency,infrared and other wireless media. Thus, the software or firmwareinstructions may be delivered to a user or a system via a communicationchannel such as a telephone line, a DSL line, a cable television line, afiber optics line, a wireless communication channel, the Internet, etc.(which are viewed as being the same as or interchangeable with providingsuch software via a transportable storage medium). The software orfirmware instructions may include machine readable instructions that,when executed by the processor, cause the processor to perform variousacts.

When implemented in hardware, the hardware may comprise one or more ofdiscrete components, an integrated circuit, an application-specificintegrated circuit (ASIC), a programmable logic device (PLD), etc.

While the present invention has been described with reference tospecific examples, which are intended to be illustrative only and not tobe limiting of the invention, changes, additions and/or deletions may bemade to the disclosed embodiments without departing from the scope ofthe invention.

What is claimed:
 1. A method, comprising: generating, at a communicationdevice, a physical layer (PHY) data unit for transmission via acommunication channel, including generating orthogonal frequencydivision multiplexing (OFDM) symbols to be included in the PHY dataunit, wherein generating each of some of the OFDM symbols includes:encoding, at a communication device, information bits to be included inthe OFDM symbol to generate two or more low density parity check (LDPC)code words to be included entirely in the OFDM symbol; parsing, at thecommunication device, content of the two or more LDPC code words into aplurality of data streams; for each data stream: parsing, at thecommunication device, the data stream into a first frequency segmentcorresponding to a first subband of the communication channel and asecond frequency segment corresponding to a second subband of thecommunication channel, for the first frequency segment, mapping, at thecommunication device, first content of the two or more LDPC code wordsto first constellation points corresponding to first OFDM tones in thefirst subband of the communication channel, for the first frequencysegment, reordering, at the communication device, the first OFDM tonessuch that the first content of the two or more LDPC code words isdistributed over the first OFDM tones within the first subband of thecommunication channel, for the second frequency segment, mapping, at thecommunication device, second content of the two or more LDPC code wordsto second constellation points corresponding to second OFDM tones in thesecond subband of the communication channel, and for the secondfrequency segment, reordering, at the communication device, the secondOFDM tones such that the second content of the two or more LDPC codewords are distributed over the second OFDM tones within the secondsubband of the communication channel.
 2. The method of claim 1, wherein:reordering the first OFDM tones includes reordering bits in the firstcontent prior to mapping the first content to the first constellationpoints such that, after mapping the first content to the firstconstellation points, the first content is distributed over the firstOFDM tones within the first subband of the communication channel; andreordering the second OFDM tones includes reordering bits in the secondcontent prior to mapping the second content to the second constellationpoints such that, after mapping the second content to the secondconstellation points, the second content is distributed over the secondOFDM tones within the second subband of the communication channel. 3.The method of claim 2, wherein: reordering bits in the first contentcomprises reordering first blocks of bits in the first content, eachfirst block corresponding to a constellation point among the firstconstellation points; and reordering bits in the second contentcomprises reordering second blocks of bits in the second content, eachsecond block corresponding to a constellation point among the secondconstellation points.
 4. The method of claim 1, wherein: reordering thefirst OFDM tones includes reordering the first constellation pointsafter mapping the first content to the first constellation points; andreordering the second OFDM tones includes reordering the secondconstellation points after mapping the second content to the secondconstellation points.
 5. The method of claim 1, wherein: the first OFDMtones are reordered such that adjacent blocks of bits in the firstcontent, prior to mapping the first content to the first constellationpoints, correspond to first OFDM tones that are separated in frequencyby a minimum tone distance; and the second OFDM tones are reordered suchthat adjacent blocks of bits in the second content, prior to mapping thesecond content to the second constellation points, correspond to secondOFDM tones that are separated in frequency by the minimum tone distance.6. The method of claim 5, wherein the minimum tone distance is at leastsix tones.
 7. The method of claim 1, wherein: the PHY data unit is amulti-user data unit including independent data for at least i) a firstuser and ii) a second user, wherein data for the first user is encodedusing binary convolutional coding (BCC), and data for the second user isencoded using low density parity check (LDPC) coding; and reorderingOFDM tones is performed only for OFDM tones corresponding to the seconduser.
 8. An apparatus, comprising: a wireless network interface deviceconfigured to generate a physical layer (PHY) data unit for transmissionvia a communication channel, including generating orthogonal frequencydivision multiplexing (OFDM) symbols to be included in the PHY dataunit, wherein the wireless network interface device is implemented onone or more integrated circuit (IC) devices, and wherein the wirelessnetwork interface device includes: one or more low density parity check(LDPC) encoders, implemented on the one or more integrated circuit (IC)devices, the one or more LDPC encoders configured to encode informationbits to be included in an OFDM symbol to generate two or more LDPC codewords to be included entirely in the OFDM symbol; a stream parserimplemented on the one or more IC devices, the stream parser configuredto parse content of the two or more LDPC code words into a plurality ofdata streams; a segment parser system implemented on the one or more ICdevices, the segment parser system coupled to the stream parser, whereinsegment parser system is configured to, for each data stream, parsecontent of the two or more LDPC code words into a first frequencysegment corresponding to a first subband of the communication channeland a second frequency segment corresponding to a second subband of thecommunication channel; a constellation mapping system implemented on theone or more IC devices, the constellation mapping system configured to,for each data stream: for the first frequency segment, map first contentof the two or more LDPC code words to first constellation pointscorresponding to first OFDM tones in the first subband of thecommunication channel, and for the second frequency segment, map secondcontent of the two or more LDPC code words to second constellationpoints corresponding to second OFDM tones in the second subband of thecommunication channel; and a tone ordering system implemented on the oneor more IC devices, the tone reordering system configured to, for eachdata stream: for the first frequency segment, reorder the first OFDMtones such that the first content of the two or more LDPC code words isdistributed over the first OFDM tones within the first subband of thecommunication channel, and for the second frequency segment, reorder thesecond OFDM tones such that the second content of the two or more LDPCcode words are distributed over the second OFDM tones within the secondsubband of the communication channel.
 9. The apparatus of claim 8,wherein: an output of the tone ordering system is coupled to an input ofthe constellation mapping system; and the tone ordering system isconfigured to reorder bits in the first content such that, after theconstellation mapper maps the first content to the first constellationpoints, the first content is distributed over the first OFDM toneswithin the first subband of the communication channel, and reorder bitsin the second content such that, after the constellation mapper maps thefirst content to the first constellation points, the second content isdistributed over the second OFDM tones within the second subband of thecommunication channel.
 10. The apparatus of claim 9, wherein the toneordering system is configured to: reorder first blocks of bits in thefirst content, each first block corresponding to a constellation pointamong the first constellation points; and reorder second blocks of bitsin the second content, each second block corresponding to aconstellation point among the second constellation points.
 11. Theapparatus of claim 8, wherein: an output of the constellation mappingsystem is coupled to an input of the tone ordering system; and the toneordering system is configured to reorder the first constellation pointsoutput by the constellation mapper, and reorder the second constellationpoints output by the constellation mapper.
 12. The apparatus of claim 8,wherein the tone ordering system is configured to: reorder the firstOFDM tones such that adjacent blocks of bits in the first content, priorto the constellation mapper mapping the first content to the firstconstellation points, correspond to first OFDM tones that are separatedin frequency by a minimum tone distance; and reorder the second OFDMtones such that adjacent blocks of bits in the second content, prior tothe constellation mapper mapping the second content to the secondconstellation points, correspond to second OFDM tones that are separatedin frequency by the minimum tone distance.
 13. The apparatus of claim12, wherein the minimum tone distance is at least six tones.
 14. Theapparatus of claim 8, wherein: the PHY data unit is a multi-user dataunit including independent data for at least i) a first user and ii) asecond user; the wireless network interface device further comprises oneor more binary convolutional coding (BCC) encoders implemented on the onthe one or more IC devices; and the one or more IC devices areconfigured to encode data for the first user using the one or more BCCencoders, encode data for the second user using the one or more LDPCencoders, and not apply the tone ordering system to OFDM tonescorresponding to the first user.
 15. The apparatus of claim 8, wherein:the segment parser system comprises a plurality of segment parser unitsimplemented on the one or more IC devices, each segment parser unitcorresponding to a respective data stream; the constellation mappingsystem comprises a plurality of constellation mapping units implementedon the one or more IC devices, each constellation mapping unitcorresponding to one of i) the first frequency segment data stream andii) the second frequency segment for the respective data stream; and thetone ordering system comprises a plurality of tone ordering unitsimplemented on the one or more IC devices, each tone ordering unitcorresponding to one of i) the first frequency segment data stream andii) the second frequency segment for the respective data stream.
 16. Theapparatus of claim 8, wherein the wireless network interface comprises:one or more transceivers implemented on the one or more integratedcircuits, the one or more transceivers configured to transmit thefeedback data.
 17. The apparatus of claim 16, further comprising: one ormore antennas coupled to the one or more transceivers.
 18. A tangible,non-transitory computer readable medium, or media, storing machinereadable instructions that, when executed by one or more processors,cause the one or more processors to: generate orthogonal frequencydivision multiplexing (OFDM) symbols to be included in a physical layer(PHY) data unit for transmission via a communication channel, including:encoding, according to a low density parity check (LDPC) encodingscheme, information bits to be included in an OFDM symbol to generatetwo or more LDPC code words to be included entirely in the OFDM symbol,parsing content of the two or more LDPC code words into a plurality ofdata streams, for each data stream, parsing content of the two or moreLDPC code words into a first frequency segment corresponding to a firstsubband of the communication channel and a second frequency segmentcorresponding to a second subband of the communication channel, for eachdata stream and for the first frequency segment, mapping first contentof the two or more LDPC code words to first constellation pointscorresponding to first OFDM tones in the first subband of thecommunication channel, for each data stream and for the first frequencysegment, reordering the first OFDM tones such that the first content ofthe two or more LDPC code words is distributed over the first OFDM toneswithin the first subband of the communication channel, for each datastream and for the second frequency segment, mapping second content ofthe two or more LDPC code words to second constellation pointscorresponding to second OFDM tones in the second subband of thecommunication channel, and for each data stream and for the secondfrequency segment, reordering the second OFDM tones such that the secondcontent of the two or more LDPC code words are distributed over thesecond OFDM tones within the second subband of the communicationchannel.
 19. The tangible, non-transitory computer readable medium, ormedia, of claim 18, further storing machine readable instructions that,when executed by the one or more processors, cause the one or moreprocessors to: reorder bits in the first content such that, after theconstellation mapper maps the first content to the first constellationpoints, the first content is distributed over the first OFDM toneswithin the first subband of the communication channel; and reorder bitsin the second content such that, after the constellation mapper maps thefirst content to the first constellation points, the second content isdistributed over the second OFDM tones within the second subband of thecommunication channel.
 20. The tangible, non-transitory computerreadable medium, or media, of claim 18, further storing machine readableinstructions that, when executed by the one or more processors, causethe one or more processors to: reorder the first constellation points;and reorder the second constellation points.
 21. The tangible,non-transitory computer readable medium, or media, of claim 18, furtherstoring machine readable instructions that, when executed by the one ormore processors, cause the one or more processors to: reorder the firstOFDM tones such that adjacent blocks of bits in the first content, priorto mapping the first content to the first constellation points,correspond to first OFDM tones that are separated in frequency by aminimum tone distance; and reorder the second OFDM tones such thatadjacent blocks of bits in the second content, prior to mapping thesecond content to the second constellation points, correspond to secondOFDM tones that are separated in frequency by the minimum tone distance.22. The tangible, non-transitory computer readable medium, or media, ofclaim 21, wherein the minimum tone distance is at least six tones. 23.The tangible, non-transitory computer readable medium, or media, ofclaim 18, wherein: further storing machine readable instructions that,when executed by the one or more processors, cause the one or moreprocessors to: the PHY data unit is a multi-user data unit includingindependent data for at least i) a first user and ii) a second user; andthe tangible, non-transitory computer readable medium, or media, furtherstores machine readable instructions that, when executed by the one ormore processors, cause the one or more processors to: encode data forthe first user according to a binary convolutional code, encode data forthe second user encoding, according to the LDPC encoding scheme, and notapply tone reordering to OFDM tones corresponding to the first user.